In general, a small-sized camera module is mounted in a mobile terminal such as a smartphone. In such a camera module, a lens driving device is employed (for example, PTL 1). The lens driving device has an auto-focusing function of automatically performing focusing for capturing a subject (hereinafter referred to as “AF (Auto Focus) function”), and a shake-correcting function (hereinafter referred to as “OIS (Optical Image Stabilization) function”) of correcting shake (vibration) upon capturing an image to reduce the irregularities of the image.
The auto-focusing and shake-correcting lens driving device includes an auto-focusing driving part (hereinafter referred to as “AF driving part”) for moving the lens part in the light axis direction, and a shake-correcting driving part (hereinafter referred to as “OIS driving part”) for swaying the lens part in a plane orthogonal to the light axis direction.
The AF driving part includes, for example, an auto-focusing coil part (hereinafter referred to as “AF coil part”) disposed around the lens part, and an auto-focusing magnet part (hereinafter referred to as “AF magnet part”) disposed separately from the AF coil part in the radial direction. Automatic focusing is performed by moving an AF movable part including the lens part and the AF coil part with respect to an AF fixing part including the AF magnet part in the light axis direction with use of a driving force of a voice coil motor composed of the AF coil part and the AF magnet part, for example.
Here, a lens position for bringing a subject at a smallest capture distance (a position on the most light reception side) into focus is called “macro position,” and a lens position for bringing a subject at the infinity (a position on the most imaging side) into focus is called “infinity position.” That is, the range from the macro position to the infinity position is the movable range of the AF movable part.
The OIS driving part includes a shake-correcting magnet part (hereinafter referred to as “OIS magnet part”) disposed at the AF driving part, and a shake-correcting coil part (hereinafter referred to as “OIS coil part”) disposed separately from the OIS magnet part in the light axis direction, for example. A shake correction movable part (hereinafter referred to as “OIS movable part”) including the AF driving part and the OIS magnet part is supported by a supporting member so as to be separated from a shake-correcting fixing part (hereinafter referred to as “OIS fixing part”) including the OIS coil part in the light axis direction. The OIS movable part is swayed in a plane orthogonal to the light axis direction by use of a driving force of a voice coil motor composed of the OIS magnet part and the OIS coil part, and thus shake correction is performed (so-called barrel shift system). The OIS magnet part can also serve as the AF magnet part, and with such a configuration, the size and the height of the lens driving device can be reduced.
In the lens driving device disclosed in PTL 1, an elastic supporting part (an upper leaf spring and a lower leaf spring) connects a lens holder (as a part of the AF movable part) in which the AF coil part is disposed at the outer peripheral surface, with a magnet holder (as a part of AF fixing part) in which the AF magnet part (which also serves as the OIS magnet part) is disposed. At the time of focusing, the AF movable part moves in the light axis direction until the driving force (driving power) of the voice coil motor of the AF driving part and the restoration force of the elastic supporting part are equivalent to each other, and the AF movable part is held in that state. Accordingly, a driving force corresponding to the restoration force of the lower leaf spring and the upper leaf spring in the maximum displacement state is required for the voice coil motor of the AF driving part.
In addition, in the lens driving device disclosed in PTL 1, in an non-energization state where focusing is not performed, the lens holder is pushed up to the light reception side in the light axis direction with a spacer disposed on the imaging side of the lower leaf spring, and a back tension is caused in the upper leaf spring and the lower leaf spring (see FIG. 2 of PTL 1). That is, the AF movable part is held at the infinity position in a non-energization state where focusing is not performed, and is moved toward the macro position in an energization state where focusing is performed.